Monochrome means one color.
Typically one color is presented in different values and intensities — or different shades of the single color.
Monochrome is a phrase often associated with older computer system monitors. Monitors, for example, can be monochrome, grayscale or color. Monochrome monitors actually use two colors, one for the display image (the foreground) and one for the background.
Graphic and digital images can also be monochrome, grayscale, or color. In photography a monochromatic image is usually in the form of a black and white photograph, which can be produced using black and white film or by removing colors in post-production.